Aliphatic amines are important organic intermediates which are prepared on a large industrial scale. For example, they are processed further to produce pharmaceutical products, agrochemicals or dyes or they serve as additive in surface-active formulations, as corrosion inhibitor and as additives in lubricants, for example in the form of their dithiocarbamates or corresponding salts, for improving the abrasion resistance of mechanical apparatuses which are operated under high pressure or as auxiliaries for the paper, textile and rubber industries. The short-chain amines having fewer than six carbon atoms per alkyl group and the fatty amines having from about 8 to 24 carbon atoms per alkyl chain are of particular industrial importance. While fatty amines were firstly produced from natural fatty acids, fatty amines have for some years also been obtained on the basis of petrochemical raw materials by processes which have become established many years ago for the preparation of short-chain amines.
Thus, the reductive amination of aldehydes and ketones by means of ammonia, primary or secondary amines leads to primary, secondary or tertiary amines. Amine formation can, for example, be described by the following reaction stages:R1—C(═O)—R2+R3NH2→R1—C(═NR3)—R2+H2O  (1)R1—C(═NR3)—R2+H2→R1—CHR2—NHR3  (2)
In the first reaction stage, an imine intermediate (R3=hydrogen) is formed by reaction of an aldehyde (R1=alkyl and R2=hydrogen) or a ketone (R1 and R2=alkyl) with ammonia or an azomethine intermediate or Schiff base (R3=alkyl) is formed by reaction with a primary amine. These intermediates are subsequently catalytically hydrogenated, either directly in one step or after isolation in the absence of water in separate reaction stages. The catalytic hydrogenation can be carried out in the presence of conventional hydrogenation catalysts such as nickel or cobalt catalysts which are activated by additions of chromium (DE 1257 782 A1, DE 2048 750 A1).
If secondary amines are reacted with aldehydes or ketones, a hydrogen atom has to be bound to the carbon atom adjacent to the carbonyl group so as to enable this hydrogen atom to be eliminated in the form of water to form an enamine. The subsequent catalytic hydrogenation then leads to tertiary amines.
If ammonia is reacted with aldehydes or ketones, primary amines are firstly formed and these then react with further aldehyde or ketone via the azomethine intermediate to form the secondary amine which can then react further in an analogous way to form tertiary amines. The product distribution can be controlled by the amount of ammonia used. Large molar excesses of ammonia promote the formation of primary amines.
Apart from the reductive amination of carbonyl compounds, the amination of alcohols or ammonolysis in the presence of hydrogen catalysts is also carried out industrially:R1—OH+HNR2R3→R1—NR2R3+H2O  (3)
If ammonia (R2 and R3=hydrogen) is reacted, a primary amine is firstly formed and this reacts further with further alcohol to form a secondary amine which can react analogously to form a tertiary amine. In this reaction, too, the product distribution can be controlled by means of the amount of ammonia used. A large molar excess of ammonia promotes the formation of the primary amine.
Suitable hydrogenation catalysts are nickel, cobalt, iron or copper catalysts, e.g. Raney nickel (U.S. Pat. No. 2,782,237, U.S. Pat. No. 2,182,807). The amination of alcohols can also be carried out in the presence of hydrogen.
Further processes for preparing amines encompass the reaction of alkyl halides with ammonia, the addition of ammonia onto olefinic double bonds, the catalytic hydrogenation of carboxylic nitriles and the catalytic reduction of nitroalkanes by hydrogen (Ullmanns Encyklopädie der technischen Chemie, 4th edition, volume 7, 1974, pages 374-389; volume 11, 1976, pages 447-452).
Isononylamine (CAS number 27775-00-4) and diisononylamine (CAS number 28454-70-8) are of industrial importance as supplement and also as additives in lubricants, for example in the form of their dithiocarbamates or corresponding salts, for improving the abrasion resistance of mechanical apparatuses which are operated under high pressure, as additive in corrosion inhibitors or for hydraulic fluids. Isononylamine contains predominantly 3,5,5-trimethylhexylamine and diisononylamine contains predominantly di(3,5,5-trimethylhexyl)amine as main isomer.
The C-9 hydrocarbon skeleton 3,5,5-trimethylhexyl is based on the petrochemical intermediate isobutene which is dimerized to diisobutene in the presence of acid catalysts and separated off by distillation from the higher oligomers which are likewise formed (Hydrocarbon Processing, April 1973, pages 171-173; Ullmann's Encyclopedia of Industrial Chemistry, 6th. Ed., 2003, Vol. 6, page 3). Diisobutene consists essentially of the isomeric octenes 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene and can be converted by means of the oxo reaction or hydroformylation reaction with carbon monoxide and hydrogen in the presence of rhodium or cobalt catalysts into the corresponding aldehyde 3,5,5-trimethylhexanal (Ullmann's Encyclopedia of Industrial Chemistry, 6th. Ed., 2003, Vol. 2, pages 68, 75; DE 2737633 A). The hydrogenation gives the alcohol 3,5,5-trimethylhexanol which is used, for example, as high-boiling solvent (Ullmann's Encyclopedia of Industrial Chemistry, 6th. Ed., 2003, Vol. 2, pages 22, 33).
The most important raw materials source for isobutene is the C4 fraction from the steam cracking of naphtha. Its availability compared to the C2 and C3 cracking products can be controlled via the conditions of steam cracking and is guided by market circumstances.
Firstly, 1,3-butadiene is removed from the C4 cracking products by extraction or by selective hydrogenation to n-butenes. The C4 raffinate obtained, also referred to as raffinate I, contains predominantly the unsaturated butenes isobutene, 1-butene and 2-butene and also the hydrogenated products n-butane and isobutane. In the next step, isobutene is removed from the raffinate I and the isobutene-free C4 mixture obtained is referred to as raffinate II.
In industrial production, the removal of isobutene is carried out using various processes in which the relatively high reactivity of isobutene in the raffinate I is exploited. The reversible proton-catalyzed molecular addition of water to form tert-butanol or the molecular addition of methanol to form methyl tert-butyl ether are known. Isobutene can be recovered again from these addition products by redissociation (Weissermel, Arpe, Industrielle Organische Chemie, VCH Verlagsgesellschaft, 3rd edition, 1988, pages 74-79).
Likewise, the butadiene-free C4 raffinate can be brought into contact with an acidic suspended ion exchanger at elevated temperature and under superatmospheric pressure. Isobutene oligomerizes to diisobutene, triisobutene and to a small extent to higher oligomers. The oligomers are separated off from the unreacted C4 compounds. Diisobutene or triisobutene can then be obtained in pure form from the oligomerization mixture by distillation. Codimer is formed to a small extent by dimerization of n-butenes with isobutene (Weissermel, Arpe, Industrielle Organische Chemie, VCH Verlagsgesellschaft, 3rd edition, 1988, page 77; Hydrocarbon Processing, April 1973, pages 171-173).
Diisobutene, either prepared by oligomerization of pure isobutene obtained by redissociation or obtained during the course of the work-up of a butadiene-free raffinate I, is subsequently converted by means of the hydroformylation reaction or oxo reaction into a C9 derivative which has one more carbon atom. Since diisobutene contains predominantly the octenes 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, the hydroformylation reaction gives the C9-aldehyde 3,5,5-trimethylhexanal as main constituent. Further C9 isomers which are present in small amounts are 3,4,4- and 3,4,5-trimethylhexanal and also 2,5,5-trimethylhexanal, 4,5,5-trimethylhexanal and 6,6-dimethylheptanal.
The isononanal prepared in this way can subsequently, as described above, be converted by reductive amination using ammonia and hydrogen into isononylamine or diisononylamine. Isononanal can also be reduced by means of hydrogen over a metal catalyst, for example over nickel or cobalt catalysts, to give isononanol and subsequently converted by means of the amination reaction into the corresponding isononylamines.
In view of the fact that the availability of octenes based on the C4 fraction from naphtha cracking is limited and depends on local site conditions, it is desirable to open up further octene sources on the basis of inexpensively available bulk products which can be transported in a simple way to the various sites. 2-Ethylhexanol is available at low cost as an industrial bulk product and can be marketed widely without problems. 2-Ethylhexanol is, as is known, prepared industrially by hydroformylation or oxo reaction of propylene to form n-butyraldehyde with subsequent alkali-catalyzed aldol condensation to form 2-ethylhexenal and subsequent total hydrogenation to 2-ethylhexanol (Ullmanns Encyklopadie der technischen Chemie, 4th edition, 1974, Verlag Chemie, volume 7, pages 214-215).
The use of 2-ethylhexanol for preparing an octene mixture which is processed by dehydration, hydroformylation and hydrogenation to give an isononanoic mixture is briefly described in WO 03/029180 A1. Here, setting of the viscosity of the isomeric dialkyl phthalates which are obtained by esterification of isomeric nonanols with phthalic acid or phthalic anhydride is the main focus. Information as to how to convert the dehydration products of 2-ethylhexanol into isononylamines is not given.
The utilization of 2-ethylhexanol as octene source makes it possible to provide isononylamines acid on the basis of propylene and reduces the dependence on the availability of octenes based on butene.